Carrier aggregation (CA) is a technique used to increase communications system bandwidth. In CA, multiple component carriers are aggregated (or combined) to yield a carrier with greater bandwidth than the individual component carriers. The component carriers may be contiguous or non-contiguous. Carrier aggregation can be considered for licensed component carriers only, or a mixture of licensed and unlicensed component carriers.
In the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) Release-12 technical standards, aggregation of up to 5 component carriers is permitted. However, in the development of subsequent releases, the number of component carriers is increased. For example, in 3GPP LTE Release-13, up to 32 component carriers may be aggregated. It is expected that the maximum allowable number of component carriers will continue to increase.